1. Field of the Invention
The present invention relates to wireless communication and, more particularly, to a method and apparatus for estimating a signal to noise ratio (SNR) in a wireless communication system.
2. Related Art
Effective transmission and reception schemes for broadband wireless communication systems and methods for utilizing the schemes have been proposed in order to maximize the efficiency of limited radio resources. One of systems taken into consideration in the next-generation wireless communication system is an orthogonal frequency division multiplexing (OFDM) system capable of attenuating an inter-symbol interference (ISI) effect with low complexity. In the OFDM system, data symbols received in series are transformed into N parallel data symbols, carried on respective subcarriers, and then transmitted. The subcarriers maintain orthogonality in the frequency dimension. The orthogonal channels experience independent frequency selective fading. Accordingly, ISI can be minimized because complexity in a receiving stage is reduced and spacing between the transmitted symbols is lengthened.
Orthogonal frequency division multiple access (hereinafter referred to as OFDMA) refers to a multiple access method of realizing multi-access by independently providing each user with some of available subcarriers in a system using OFDM as a modulation scheme. In general, in OFDMA, frequency resources called subcarriers are provided to each user, and the frequency resources do not overlap with each other because the frequency resources are independently to a plurality of the users. Accordingly, the frequency resources are exclusively allocated to each user.
A mobile station can estimate the signal to noise ratio (SNR) of a reception signal. The estimated SNR may be applied in various ways. Advanced modulation and coding (AMC) may be applied using the SNR, and a mobile station can stabilize link performance by reporting the SNR to a base station through a message or feedback channel in a multiple-input multiple-output (MIMO) system. Furthermore, system capacity can be improved by using a modulation scheme of a higher order.
Meanwhile, in order to precisely estimate the SNR of a reception signal, it is important to accurately calculate noise power. In general, when the distance between a mobile station and a base station is small, the intensity of the reception signal is strong. An error in the estimation of noise power is increased according to an increase in the intensity of the reception signal. Accordingly, accuracy in estimating the SNR of a reception signal having a high SNR is low.
Accordingly, there is a need for a method of more accurately estimating the SNR.